1. Field of the Invention
The present invention relates to a color liquid crystal display device for presenting color display using a backlight which emits light of a plurality of colors.
2. Description of the Background Art
A transmissive liquid crystal display device is a device such that light emitted from a backlight disposed on the backside thereof is transmitted through a liquid crystal panel and is then used to recognize an image. FIG. 25 shows an example of a sectional structure of a liquid crystal panel 100 for use in the transmissive liquid crystal display device. The liquid crystal panel 100 comprises polarizing filters 101, 102, an array substrate 103, a glass substrate 104 with a color filter 106 placed on a surface thereof, the substrates 103 and 104 being disposed in opposed relation to each other between the polarizing filters 101 and 102, and a liquid crystal layer 105 sealed in a space between the substrates 103 and 104. Although not shown, pixel electrodes and active elements are disposed in a matrix on a surface of the array substrate 103, and transparent electrodes opposed to the pixel electrodes are formed between the color filter 106 and the liquid crystal layer 105. A backlight 107 which emits white light 108 is provided on the backside of such a liquid crystal panel 100. The white light 108 is colored when passing through the color filter 106 of the liquid crystal panel 100. As shown in FIG. 26, the color filter 106 has R (red), G (green) and B (blue) colored layers corresponding to each pixel and disposed in a matrix on the glass substrate 104. Each of the colors for each pixel corresponds to one liquid crystal cell.
Also known is another transmissive liquid crystal display device which employs backlights 206R, 206G and 206B for emitting light of three colors R, G and B, respectively, as shown in FIG. 27. A liquid crystal panel 200 shown in FIG. 27 comprises polarizing filters 201, 202, an array substrate 203 and a glass substrate 204 which are disposed in opposed relation to each other between the polarizing filters 201 and 202, and a liquid crystal layer 205 sealed in a space between the substrates 203 and 204. The remaining structure of the liquid crystal panel 200 is substantially similar to the corresponding structure shown in FIG. 25 except that the liquid crystal panel 200 comprises no color filter. The backlights 206R, 206G and 206B disposed on the backside of such a liquid crystal panel 200 are controlled to turn on in a time-shared manner for each emitted color. As shown in FIG. 28, each pixel of the liquid crystal panel 200 corresponds to one liquid crystal cell. Thus, the liquid crystal panel 200 is required to have liquid crystal cells the number of which is one third the number of liquid crystal cells of the liquid crystal panel 100 of the color filter type shown in FIG. 25 under the same specifications. The liquid crystal panel 200 has the advantage of greatly reducing light losses because of the non-use of the color filter, to require a smaller amount of backlight to achieve the same intensity of the transmitted light as that of the color filter type.
FIGS. 29 and 31 are schematic diagrams of background art transmissive liquid crystal display devices using a backlight for emitting light of three colors R, G and B. A liquid crystal display device 300 shown in FIG. 29 is disclosed in Japanese Patent Application Laid-Open No. 2000-28984. In FIG. 29, the reference numeral 301 designates a liquid crystal panel using ferroelectric or antiferroelectric liquid crystal elements capable of high-speed response; 302 designates a backlight having a group of LEDs (Light-Emitting Diodes) for emitting light of each of the colors R, G and B; 305 designates a source driver for driving signal lines of the liquid crystal panel 301; and 306 designates a gate driver for selectively driving scanning lines of the liquid crystal panel 301. Light emitted from the backlight 302 is directed through a light guide plate (not shown) onto the backside of the liquid crystal panel 301. Display data DD for display on the liquid crystal panel 301 is inputted to an image memory 303 from, for example, a personal computer. The image memory 303 temporarily stores therein the inputted display data DD, and then outputs data (referred to hereinafter as pixel data PD) for each pixel in synchronism with a synchronizing signal SYN provided from a control signal generating circuit 304. The pixel data PD is transmitted to a first input terminal of a selector 310 and to an inverted data generating circuit 309.
The control signal generating circuit 304 generates the synchronizing signal SYN to output the synchronizing signal SYN to the gate driver 306, a reference voltage generating circuit 307 and a backlight control circuit 308 including a drive power supply. The gate driver 306 controls the on/off operation of the scanning lines of the liquid crystal panel 301 in synchronism with the synchronizing signal SYN. The reference voltage generating circuit 307 generates a reference voltage VR in synchronism with the synchronizing signal SYN to provide the reference voltage VR to the source driver 305 and the gate driver 306. The backlight control circuit 308 provides a drive voltage synchronous with the synchronizing signal SYN to the backlight 302 to cause the LEDs constituting the backlight 302 to emit light. FIG. 30A is a timing chart showing the lighting timing of the backlight. The backlight 302 emits R light, G light and B light corresponding to an R subframe, a G subframe and a B subframe, respectively, in a time-shared manner during one frame display period ({fraction (1/60)} second). FIG. 30B is a timing chart showing a data write scanning signal and a data erase scanning signal in timed relation to the lighting of the LEDs of the three colors shown in FIG. 30A.
The inverted data generating circuit 309 produces inverted data #PD which is an inverted version of the pixel data PD to output the inverted data #PD to a second input terminal of the selector 310. The selector 310 selects one of the pixel data PD and the inverted data #PD in accordance with a control signal CS transmitted from the control signal generating circuit 304 to output the selected data to the source driver 305. The source driver 305 provides a voltage signal corresponding to the pixel data PD or the inverted data #PD through the signal lines of the liquid crystal panel 301 to the pixel electrodes. When the voltage signal corresponding to the inverted data #PD is provided, an electric field equal in intensity to but opposite in polarity from an electric field applied during data write scanning is applied to the pixel electrodes of the liquid crystal panel 301 during data erase scanning shown in FIG. 30B to erase (or turn off) display of pixels.
One of the features of a display control method for the liquid crystal display device 300 lies in producing a difference in time interval of light emission from the backlight 302 between at least two of the colors R, G and B. Additionally, the time intervals of light emission from the backlight 302 are not constant for the respective colors, and a scanning signal is provided so as to correspond to a light emission sequence in which the light emission time intervals are adjusted depending on the light emission intensities of the LEDs of the respective colors. Thus providing variable control of at least one of the light emission time interval of and the light emission intensity of the LEDs of each color of the backlight 302 allows adjustment of chromaticity of a display color and a wide range of color balance adjustment.
A background art liquid crystal display device 311 shown in FIG. 31 is disclosed in Japanese Patent Application Laid-Open No. 2000-147454. The liquid crystal display device 311 is substantially similar in functionality to the liquid crystal display device 300 shown in FIG. 29 except for the structure of the backlight 302 and the light emission control method for the backlight 302. Elements in FIG. 31 designated by the same reference numerals and characters as those shown in FIG. 29 are substantially identical in functionality with those of the liquid crystal display device 300. The liquid crystal display device 311 is intended to suppress the unevenness of brightness within a display region of the liquid crystal panel 301, and features optically dividing a light emission region of the backlight 302 into a plurality of blocks 3021, 3022 and 3023 having different light emission intensities.
Unfortunately, the background art liquid crystal display devices 300 and 311 are incapable of controlling a change in display order of subframes for the input display data DD and of controlling the xe2x80x9conxe2x80x9d period and display brightness of the LEDs for each color. When a liquid crystal panel having a relatively low response speed exceeding about 100 microseconds is used, it is important to control the lighting of the backlight at the time of a change between subframes and to control the timing of writing of image data into the liquid crystal panel. However, the liquid crystal display devices 300 and 311 are based on the premise that the devices 300 and 311 employ the ferroelectric or antiferroelectric liquid crystal material capable of high-speed response. Therefore, the above-mentioned background art applications do not disclose the control of the lighting of the backlight and the control of timing of data writing.
It is an object of the present invention to provide a liquid crystal display device capable of controlling the writing timing of image data into a liquid crystal panel and the lighting timing of a backlight to improve the quality of a display image and a display brightness.
According to the present invention, a liquid crystal display device includes a transmissive liquid crystal display panel devoid of any color filter, an image data processor, a driver circuit, a backlight, a backlight controller, a judging circuit, and a controller. The image data processor converts one frame of an image including a plurality of color components into a plurality of subframes each consisting of a single color component to output the subframes in predetermined order. The driver circuit drives the liquid crystal display panel based on the subframes received from the image data processor. The backlight illuminates a backside of the liquid crystal display panel, and includes a light source for emitting light of a plurality of colors. The backlight controller controls the backlight to turn on to emit light of a color corresponding to a color component of each of the subframes in a time-shared manner in synchronism with the time at which the driver circuit writes each of the subframes into the liquid crystal display panel. The judging circuit calculates difference data between adjacent ones of the subframes which are successive in display order on a pixel-by-pixel basis to judge whether or not there is a subframe-to-subframe difference therebetween on a line-by-line basis, based on the difference data for one line. The controller temporarily shortens a write cycle duration of a clock for defining the timing of writing of image data for a line judged by the judging circuit to be devoid of the subframe-to-subframe difference into the liquid crystal display panel. The driver circuit reduces a pulse width of an address signal to be applied to a scanning line of the liquid crystal display panel in accordance with the write cycle duration.
The liquid crystal display device can judge whether or not the difference between the subframes successive in display order is large on a line-by-line basis, and substantially skip the writing of image data for a line judged to be devoid of the difference. This reduces the display period of the subframes. Additionally, the liquid crystal display device reduces a time lag between the xe2x80x9conxe2x80x9d period of the backlight and the display period of the image data to display a high-quality image with improved contrast and hue.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.